704 PROCEEDINGS OF THE ACADEMY OF [DeC. , 



that run along the ventral blood connectives. The wall of the 

 ductule is a one-celled layer and encloses a narrow lumen. The 

 cells are wider than high, with but little cytoplasm and elongated 

 nuclei. The cell surface turned toward the lumen bears cilia. No 

 basement membrane is present. 



About 3-4 mm. behind the first appearance of the terminal bulbs 

 the main nephridial duct begins, fig. 46, Nph.D. It is situated on 

 the ventral side of the lateral blood vessel, in the angle made by 

 the junction of the ventral connective with the lateral vessel; the 

 main duct does not project into the blood vessel, but merely adjoins 

 it with one surface, the other surfaces being surrounded by the fibres 

 of the inner longitudinal muscle layer. The main duct is about 2 

 mm. long and composes the greater part of the nephridium. Into its 

 anterior end for some little distance the ductules open, but behind 

 that there are no diverticula until the excretory duct at the pos- 

 terior end is reached. The main duct is thick-walled, fig. 46, and 

 slightly convoluted throughout its length. The cells of the wall 

 are considerably higher than wide, with quite sharply defined cell 

 membranes. The nuclei are prominent and are situated near the 

 outer or basal side of the cell, i.e., away from the lumen of 

 the duct. The outer surfaces of the cells are usually irregular, 

 and often bear amoeboid processes, no basement membrane being 

 present. The surface bordering on the lumen is ciliated, and the 

 liasal knobs of the cilia are very distinct. 



In the cells of the main duct and ductules of one specimen 

 that had been fixed in a solution of sublimate in 50 per cent, 

 alcohol, and stained with hjeraatoxyliu and eosin, were found 

 numerous prominent red-staining bodies of the same size as the 

 nucleus, but neither larger nor smaller ones. Wherever these red 

 bodies occurred they were found one to a cell, and at first it seemed 

 as if they were degenerating nuclei. Careful examination, how- 

 ever, detected the nucleus in each cell, of normal size, but 

 staining less deeply than usual. It is possible that these bodies 

 may be excretory masses, but their absence from the lumen 

 of the duct and the fact that no intermediate stages in their for- 

 mation have been seen would discredit this view. Burger (1890), 

 p. 93, describes in the uephridia of Carinella what may be simi- 

 lar masses: " Schon in den Zellen der .... Endkaniilchen und 

 Eudkolben, fielen mir bis kerngrosse glunzende griine Konkremente 



